AbstractA flow‐through coulometric titration technique is described which can be applied for the determination of a wide variety of compounds. If necessary, the sample can be transformed in the measuring system into a form which can be titrated. Thus an enzyme‐catalyzed reaction can also be used as a sample pretreatment step. In this article a measurement technique and apparatus are described in which an enzyme‐catalyzed reaction is used for the fast and reliable determination of penicillin compounds. The principle of the technique is that an enzyme reactor is built into the sample line of the measurement system used for performing coulometric triangle programmed titrations. One of the components of the reaction mixture leaving the reactor (in this case penicilloic acid) is determined by coulometric acid–base titration. This technique is especially useful for the analysis of large sample series.